Big Muff Pi, rehouse and 9v

Ok so I want to rehouse my Russian Big Muff into a Hammond 1590 enclosure and I have a couple questions.

For the 9v mod do I just cut the leads from the battery and solder them to the DC jack, along with the grounding that goes from the case to the negative of the DC jack. I'll be using the plastic 2.1 mm DC jacks.

Or do I need to reverse the +/- or something like that, I've read that there can be polarity or grounding issues, especially with daisy chain.

As for the jacks, I guess I need a stereo for input and just mono for output, right? Do I need to worry about grounding to the enclosure or anything like that?

the existing jacks are crappy plastic pieces that are soldered to the board. they are plastic so I'm wondering if I will have grounding issues if i switch them to metal ones that make contact with the enclosure. I will have to take them off in order to fit it in the new enclosure.